1. Field of the Invention
The present invention relates to a light source of a non-self-luminous display device, and more particularly to a liquid crystal display device having a backlight which includes a light guide plate and uses an LED as a light source.
2. Background Art
Recently, the liquid crystal display device has been popularly used as a display device. Particularly, the liquid crystal display device is used as a display part of portable equipment because the liquid crystal display device is thin and light-weighted, and consumes small electric power.
However, the liquid crystal display device is not self-luminous and hence, the liquid crystal display device requires a lighting means. In general, as a lighting device which is used for the liquid crystal display device, a planar lighting device referred to as a backlight is popularly used. Conventionally, although a cold cathode discharge tube has been used as a light emitting element (also referred to as a light source) of the backlight, an LED (light emitting diode) has been also recently used as the light emitting element.
As a thin backlight, there has been known a side-light-type backlight which includes a light emitting element on a side surface thereof. The side-light-type backlight includes a plate-shaped light guide plate. A material of the light guide plate is a light transmitting resin or the like, and light incident on the light guide plate from the light emitting element propagates in the inside of the light guide plate. A reflection/scattering member such as grooves, projections or a printed material is formed on the light guide plate, and the light which propagates in the inside of the light guide plate due to such a reflection/scattering member is directed and radiated toward a liquid-crystal-display-device side.
When LEDs are used as a light emitting element, there arises a drawback that a thickness of the LED becomes larger than a thickness of the light guide plate. Accordingly, in JP-A-2004-12747 (patent document 1), for example, there has been proposed a light guide plate having the constitution in which the light guide plate has a large thickness at a light incident surface on which light is incident from a light source and sets a thickness thereof at a light radiating surface smaller than the thickness of the light guide plate at the light incident surface. Further, in patent document 1, there has been also proposed a light guide plate having the constitution in which a thickness of a light guide plate is set in two stages by forming an inclined surface which extends toward a light radiating surface from a light incident surface. However, patent document 1 neither discloses nor suggests a manufacturing method of the light guide plate whose thickness is further reduced at the light radiating surface.
On the other hand, JP-A-2001-341177 (patent document 2) discloses a technique which forms a light guide plate by compressing a resin at the time of forming the light guide plate by injection molding. However, in the technique disclosed in patent document 2, the whole light guide plate is compressed so that a portion to be compressed is not limited to the light incident portion. Further, patent document 2 neither discloses nor suggests a method of taking out the light guide plate which is suitable for the mass production.